The Stem Cell Core will provide two main functions for the Gene Therapy Program Projects. Marrow, peripheral blood and cord blood pluripotent hematopoietic stem cells (PHSCs) will be isolated by monoclonal antibody staining and fluorescence activated cell sorting. In addition, this core will perform in vitro and in vivo assays to detect pluripotent hematopoietic stem cells. These assays will include in vitro long term bone marrow cultures which detect the long-term culture-initiating cell which is the best qualitative in vitro assay for PHSCs. In addition, both the SCID-hu bone and thymus will serve as in vivo assays of PHSC function. Analysis of BFU-E cloned from the long-term marrow cultures and red blood cells isolated from IL-3 and erythropoietin primed SCID-hu bone assays will allow us to determine if new genes are being successfully transferred into erythroid cells which originate from transduced PHSCs. This core will also provide advice in training investigators that require access to flow cytometry or as says of hematopoietic progenitor or stem cells.